LEAF AREA INDEX (LAI) OF LOBLOLLY PINE AND EMERGENT VEGETATION FOLLOWING A HARVEST

摘要

Forests provide goods and services to society and, often, refugia for plants and animals; forest managers utilize silviculture to provide ecosystem services and to create habitat. On the Coastal Plain of North Carolina, forest management objectives typically include wood fiber production but may also include the maintenance of environmental quality and, sometimes, species diversity. Silvicultural prescriptions alter stand structure and development trajectories by influencing the competitive interactions among plant species for site resources. Early site intervention may include nutrient additions and/or vegetation control; in coastal loblolly pine (Pinus taeda L.) stands, herbaceous and arborescent species can dominate the site leaf area index (LAI) for many years after a harvest (followed by planting). LA] is an important structural and functional component of a forest stand. Many eco-hydrologic and water quality models do not accurately account for LAI as the process driver to evapotranspiration (ET), and thus they ignore the ecophysiological effects of LAI on site water balance and nutrient loading. We measured LAI of emergent vegetation following a harvest, mechanical site preparation, and then pine planting for a drained loblolly pine plantation in coastal North Carolina. For six years monthly, growing season estimates of LAI were obtained using a LI-COR LAI 2000 Plant Canopy Analyzer (PCA) for control (D1), thinned (D3), and harvested (D2) watersheds. In this article, we present results from the D2 treatment. In D2, we "harvested" all emergent vegetation in 18 randomly placed 1 m(2) clip plots for three growing seasons where we estimated LAI using species-pooled estimates of specific leaf area and total leaf dry mass (i.e., LAI(CLIP)); PCA measurements were recorded prior to clipping (LAI(PCA)). We also simulated loblolly pine seedling growth and development using the biogeochemical process model SECRETS-3PG to examine site differentiation in LAI. Four years post-harvest maximum LAI(CLIP) exceeded 8 m(2) m(-2) (projected area basis). LAI(PCA) underestimated LAI(CLIP); LAI(CLIP) = 1.436 X LAI(PCA) (r(2) = 0.53; p < 0.0001; n = 195). Corrected LAI(PCA) estimates exceeded simulated pine LAI (LAI(SIM)) for similar to 4.5 years post-planting. Emergent vegetation dominated the site for nearly five years and likely exerted a strong influence over site water balance and nutrient use during early stand development.